“Forests are in deep trouble,” said Ron Neilson, a Forest Service
bioclimatologist and a professor at Oregon State University.

“Tom Coleman, the Forest Service entomologist who announced the
discovery of the oak borer in August …”The very worst-case scenario
is that we see a massive die-off of our hardwood forest. . . .”

“The same dynamic is at play everywhere on the planet,” Neilson said.

“In Central California, forests have been scourged by a disease
called sudden oak death since the mid-1990s. British Columbia has
been hammered by red band needle blight. Forestry experts say heavy
summer rains promoted the spread of both infections.

“In Alaska, the deaths of millions of yellow cedars are linked to
earlier snowmelt, which exposes shallow roots to spring freezes.”
————————————–

Bugs and diseases are killing trees at an alarming rate across the
West, from the spruce forests of Alaska to the oak woodlands near the
San Diego-Tijuana border.

Several scientists said the growing threat appears linked to global
warming. That means tree mortality is likely to rise in places as the
continent warms, potentially altering landscapes in ways that
increase erosion, fan wildfires and diminish the biodiversity of
Western forests.

It also could prompt new approaches to forestry. Possibilities
include replanting logged areas with trees that are tolerant of
higher temperatures, thinning drought-stressed forests and deploying
pesticides to ward off insects.

But in many cases, landowners have few options to protect their trees
once insects and diseases take hold, tree experts said.

One serious problem is emerging in San Diego County. U.S. Forest
Service officials recently announced that a newcomer called the
gold-spotted oak borer has infested a larger area than they thought
just a few months ago. The beetle could easily march north into more
of the estimated 33 million forested acres statewide.

The pest already is blamed for killing more than 10,000 oaks in the
county. Some backcountry residents fear the worst is yet to come
unless the drought is broken by years of heavy rain, but that’s
unlikely to happen. Climate models show the Southwest becoming
increasingly warm and dry over the next century, conditions that
leave the Cleveland National Forest and others vulnerable.

“Forests are in deep trouble,” said Ron Neilson, a Forest Service
bioclimatologist and a professor at Oregon State University. “It’s
like tripping dominoes. The trees get dry and then the bugs come in
and cause the whole ecosystem to collapse, and that can also be
followed by fires.”

Insects and disease are a normal, even critical, part of the forest
life cycle because they help break down plants and put nutrients back
into the soil. However, they appear to be getting the upper hand in a
growing number of forests because of heat and drought stress, Neilson
and others said.

“The same dynamic is at play everywhere on the planet,” Neilson said.

Drought-stressed trees can’t fend off pests and pathogens like
healthy trees can, according to an August report by several federal
scientists.

The report said that from 1997 to 2003, insect-and disease-caused
tree mortality quadrupled to 12.2 million acres in the United States.
It also said the amount of forest land hit by bugs and disease each
year is far greater than the amount that burns in wildfires.

The national numbers have dropped since 2003, but they remain far
above the levels reported in the late 1990s, according to the most
recent federal data.

Scientists said the effect of climate changes on forests is
compounded by other factors, including decades of fire suppression
that have left some forests too dense for the water available.

“For as long as people have been looking at such things, we have
never had the series of attacks on forest health all occurring at the
same time that we are currently experiencing,” said Alex Woods, a
forest pathologist in British Columbia.

Of particular concern in the West are bark beetles, a large group of
insects that includes some very aggressive species.

“Several of the current bark-beetle outbreaks across North America
are the largest and most severe in recorded history,” said Barbara
Bentz, an entomologist for the Forest Service in Utah.

In British Columbia, mountain pine beetles have infested more than 30
million acres.

Bark beetles in Southern California reached epidemic proportions five
years ago, when they killed drought-stressed trees across tens of
thousands of acres and provided fuel for the catastrophic wildfires
of 2003.

Over the past six years, the number of invasive bark beetles detected
in California has doubled to 20 species. Scientists expect the trend
to continue as insects from Mexico and the Southwest spread north.

“We are starting to pick up more cases of Mexican insects coming to
the U.S. It really does suggest there’s a pattern” related to
climate, said Steven Seybold, who studies insects for the Forest
Service in Davis.

In some places, slightly warmer winters allow more insects to survive
from one year to the next. In others, warmer summers give the bugs a
chance to reproduce more quickly. Researchers also report that
insects are moving higher up the mountains because they can survive
in areas that used to be too cold.

“For many of these large-scale infestations, the trigger has been the
change in weather conditions,” said Chris Fettig, a researcher with
the Forest Service in Davis.

In San Diego County, the spread of the oak borer is a mounting
concern. The metallic-green insect has hit particularly hard in and
around Pine Valley, Laguna Mountain, Descanso and Cuyamaca Rancho
State Park.

“There are dead trees all over the place,” said Bret Hutchinson, who
runs a tree-service company in North County. “Drought has weakened
the trees, and beetles are getting in there and spreading disease.
It’s a never-ending whirlwind of Mother Nature doing her thing, and
we are stuck in the middle.”

Tom Coleman, the Forest Service entomologist who announced the
discovery of the oak borer in August, said the beetle probably
arrived in the county on a shipment of firewood from Mexico.

Coleman and his colleagues are looking for ways to contain the
insect’s spread, but their options are limited by the Cleveland
forest budget – which doesn’t include specific funding for oak borers
in 2009 – and other constraints.

Forest leaders said they expect to receive money from the service’s
California office once they have firm action plans. They recently
banned taking oak firewood from the forest’s Descanso Ranger
District, but they can’t control the movement of wood from private
property. They have talked about other measures, including the
removal of dead trees.

Despite such efforts, Cleveland National Forest spokesman Brian
Harris is concerned that the larvae could hatch across the region in
the spring.

“The very worst-case scenario is that we see a massive die-off of our
hardwood forest. . . . That level of dead fuels is something we don’t
want to see,” he said.

Beetles are the highest-profile tree pest in many places, but they
aren’t the only threat.

In Central California, forests have been scourged by a disease called
sudden oak death since the mid-1990s. British Columbia has been
hammered by red band needle blight. Forestry experts say heavy summer
rains promoted the spread of both infections.

In Alaska, the deaths of millions of yellow cedars are linked to
earlier snowmelt, which exposes shallow roots to spring freezes.

Neilson of the Forest Service said he hopes the dire situation will
force conservationists, regulators and timber companies to agree on
plans to thin drought-stressed landscapes and reduce the chances for
more catastrophic insect and disease infestations.